Dr. Wayne Harrington, an oral surgeon with a practice in Tulsa, Okla., is being investigated by the state dental board, the state bureau of narcotics and the federal Drug Enforcement Agency because one of his patients recently tested positive for hepatitis C and HIV without known risk factors other than receiving dental treatment.

Among the 7,000 patients who may have been exposed to HIV and Hepatitis in an Oklahoma dentist's office are children, as their nervous parents wait to get them tested and grapple with how to explain the public health nightmare.

Deann Zavala took her four children to Dr. Wayne Scott Harrington, an oral surgeon who practices in Tulsa and Owasso. She said her youngest daughter had a tooth extracted.

"How do you look at her and be like, 'You could have AIDS?'" she told ABC News Radio.

The state dental board is offering free testing to Harrington's patients after a 17-count complaint revealed his allegedly poor sterilization practices could have put them at risk for contracting HIV, hepatitis C, and hepatitis B.

Patients received a letter from the Tulsa Health Department on Friday informing them of an inquiry into Harrington's practice and advising them to get screened.

Zavala, who said she trusted Harrington to care for her four children, was left shaken.

"If you can't trust a doctor and a dentist and ... the people that are supposed to do right by you ... who can you trust?" she said.

The dentist's alleged practices came to light after a patient who had no known risk factors other than receiving dental treatment in Harrington's office, tested positive for both HIV and hepatitis C.

"I could not believe it because I had just been there Feb. 28," Linda Grimm, a patient of Harrington's, told ABC News' Tulsa affiliate KTUL. "My worry now is my health issues that may develop."

After hearing about the infected patient on March 15, the Oklahoma Board of Dentistry conducted a surprise investigation of the dentist's practice on March 18, allegedly finding numerous sterilization and cross-contamination issues.

Investigators found two different sets of instruments -- one set for patients known to have infectious diseases, and another set for patients who were not believed to have infectious diseases.

Investigators also found that the autoclave, the machine designed to sterilize dental instruments meant to be tested each month, hadn't been checked in six years.

"We were just physically kind of sick," said Susan Rodgers, president of the Oklahoma Board of Dentistry. "The instruments that came out of the autoclave were horrible. I wouldn't let my nephews play with them out in the dirt." '

Harrington, who has been practicing for more than 30 years, may face criminal charges. The dentist voluntarily surrendered his state dental license and other permits, and a formal hearing before the dentistry board is scheduled for April 19.

ABC News' Phoenix affiliate KNXV went to a home believed to be owned by Harrington in Carefree, Ariz. on Friday. A man believed to be Harrington declined to comment, and slammed the door.

Harrington and his staff told investigators that he treated a "high population of known infectious disease carrier patients," according to a 17-count complaint filed by the Oklahoma Board of Dentistry.

Drug cabinets were unlocked and unsupervised during the day, and Harrington did not keep an inventory log of drugs, some of which were controlled substances, according to the complaint. One drug vial expired in 1993.

"During the inspections, Dr. Harrington referred to his staff regarding all sterilization and drug procedures in his office," the complaint read. "He advised, 'They take care of that. I don't.'"

Harrington allegedly re-used needles, contaminating drugs with potentially harmful bacteria and trace amounts of other drugs, according to the complaint. Although patient-specific drug records indicated that they were using morphine in 2012, no morphine had been ordered since 2009.